Scientists poised to drill into fault

One of New Zealand's biggest science experiments has been cleared to start in three weeks.

Preparations for drilling into the South Island's Alpine Fault on the West Coast are expected to begin on January 24.

Scientists from Otago University's geology department, Crown research institute GNS Science and Victoria University's school of geography, environment and earth sciences applied for a 30-year Department of Conservation (DOC) concession to drill at one of two West Coast sites.

DOC said before Christmas it received no submissions from the public on the researchers' preferred site for the multimillion-dollar Deep Fault Drilling Project on the Gaunt Creek river flats in the Waitangi Forest Conservation Area near Whataroa.

A track will need to be bulldozed across conservation land to allow scientists to carry out the project.

Scientists had also proposed a "backup" site by the Waikukupa River bridge on State Highway 6, between the Franz Josef and Fox Glacier townships, in the Westland Tai Poutini National Park.

Researchers hope to drill two boreholes about 150 metres deep and about 50m apart where the fault crosses the river flats.

They are also considering a 1.5km-deep borehole at a yet-to-be-determined location.

The Alpine Fault, the boundary between the Pacific and Australian crustal plates, extends more than 650 kilometres from Marlborough along the western edge of the Southern Alps to Milford Sound.

Researchers believe it ruptures every 200 to 400 years, producing magnitude-8.0 earthquakes. It last moved in 1717 in an earthquake that split up to 400km of the fault.

The September 4 magnitude-7.1 Canterbury quake caused a 29km-long surface rupture of the hidden Greendale Fault.

The Alpine Fault is seen as a unique natural laboratory because underground rocks are being pushed up rapidly along the fault due to erosion of the Southern Alps by torrential West Coast rainfall.

Project manager Dr Rupert Sutherland, of GNS Science, said it was still not known how a major earthquake on the Alpine Fault would occur.

"The Canterbury earthquake highlights the importance of understanding our earthquake hazards.

"We know the Alpine Fault represents a much larger hazard than the fault at Darfield, but what will happen when it ruptures?

"It is not a given that the human effects will be worse than the Darfield event.

"Compare, for example, the magnitude-7.8 Dusky Sound earthquake of July 2009, which was the largest earthquake in New Zealand since the magnitude-7.8 Napier earthquake in 1931.

"It was a much larger earthquake than in Canterbury, but with very limited consequences.

"We simply don't know what the character of an earthquake on the Alpine Fault will be."

Understanding the South Island's largest earthquake hazard would help plan an appropriate and cost-effective response for when it eventually ruptured, Sutherland said.

"The exact probability of this rupture is the subject of ongoing research, but various preliminary estimates place it in the range of 20 to 40 per cent in the next 30 years, so it is clearly worth spending some effort on."

Scientists from Britain, Germany, Canada, the United States and possibly Japan also were expected to take part in the project, he said.

Funding had been granted from Britain, Germany and from the Marsden Fund in New Zealand, along with contributions from GNS Science and Victoria, Otago, Canterbury and Auckland universities.

As well as analysing rocks from the boreholes, scientists will lower devices into the holes to determine how rocks have been broken and altered.

They also hope to install a long-term observatory on top of the fault zone.

The Press